Giải bài 30 trang 19 - SGK Toán lớp 7 Tập 1

a) \(x : \left(-\dfrac{1}{2} \right)^3 = -\dfrac{1}{2}\)
\(\Leftrightarrow x = \left(-\dfrac{1}{2} \right).\left(-\dfrac{1}{2} \right)^3\)
\(\Leftrightarrow x = \left(-\dfrac{1}{2} \right)^4 = \dfrac{1}{16} \)
b) \(\left(\dfrac{3}{4} \right)^5 . x = \left(\dfrac{3}{4} \right)^7\)
\(\Leftrightarrow x = \left(\dfrac{3}{4} \right)^7 : \left(\dfrac{3}{4} \right)^5\)
\(\Leftrightarrow x = \left(\dfrac{3}{4} \right)^2 =\dfrac{9}{16}\)

Lưu ý: 
\(+ \,\,\,\, a^m : a^n = a^{m - n};\,\,a \ne 0, \, m \geq 0\\ + \,\,\,\, a^m.a^n = a^{m + n} \)